Hello Hamish, have you got a minimal query example of what you have tried? It's not clear what query language you use, and within that, what you have tried. For example, SQL has GROUP BY which allows grouping by unique values of a column (whether you filter on it or not).
There's indeed a record limit count both in Canvas (that you can specify with a higher value) and at the Elasticsearch level (which requires changes to the elasticsearc.yaml configuration)